review(#1660, #1663): associative sweep scan, arc angles, viewport off bit

- refresh_associative_sweeps runs on every edit and scanned the xdata of
  every entity; it now returns at once when no associative swept surface
  exists (its application is not registered) and looks at surfaces only.
- An arc's end angle was raised by TAU in a loop, which never ends on a
  huge angle from a damaged file; the sweep is taken with rem_euclid.
- The sweep DELOBJ test expected surface sweeps to delete their sources,
  which #1663 changed on purpose: an associative surface keeps them.
- codec c9ffcac (opencadcodec #103) adds an explicit viewport-off bit: the
  viewport on state is read with is_on() and set with turn_on()/turn_off()
  everywhere, so a viewport the file marks off shows off and can be turned
  back on from Properties.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/scene/project.rs

@@ -21,7 +21,7 @@ impl Scene {
             })
             .filter(|vp| {
                 vp.common.owner_handle == paper_block
-                    && vp.status.is_on
+                    && vp.is_on()
                     && only_vp.map_or(true, |h| vp.common.handle == h)
                     && exclude_vp.map_or(true, |h| vp.common.handle != h)
             })
@@ -439,7 +439,7 @@ impl Scene {
             .iter()
             .filter_map(|handle| match self.document.get_entity(*handle) {
                 Some(EntityType::Viewport(viewport))
-                    if viewport.common.owner_handle == paper_block && viewport.status.is_on =>
+                    if viewport.common.owner_handle == paper_block && viewport.is_on() =>
                 {
                     Some(viewport)
                 }